Three things make public restrooms especially worrisome during the COVID-19 crisis.

First of all, they are small, enclosed spaces, which help spread the virus. Secondly, you’re sharing that space with strangers. Finally, there’s the toilet plume, the cloud of tiny particles that are expelled into the air every time a toilet is flushed without closing the lid.

Researchers in China discovered that flushing a toilet creates an aerosol cloud that may contain virus droplets. They used a computer simulation to show how the coronavirus may spread if you don’t close the toilet lid before flushing.

According to the New York Post, a study conducted by the Association for Professionals in Infection Control and Epidemiology also discovered this dangerous transmission and recently published their results.

“Close the lid and then flush,” advised Dr. Qingyan Chen, a mechanical engineering professor from Purdue University. Chen said that closing the lid can prevent 80% of the fecal particles from escaping into the air.

According to Bustle.com, researchers at the University of Leeds in 2012 found that germs can be hurled up to 10 inches into the air every times a toilet is flushed without closing the lid.

Recently, according to Self, researchers found that even urinals produce aerosol particles. A study published in the journal Physics of Fluid found “an alarming upward flow with strong turbulence can be generated,” sending potentially virus-packed urine aerosols into the air.

Experts say that one easy way to reduce this potential threat is to close the lid before you flush and wear a mask whenever you are in a public bathroom. The National Institutes of Health recommends that you “flush and run,” especially if the public toilet doesn’t have a lid or if you are using a urinal. Wash your hands before and after using the restroom, according to Self.